ACTIVE PHOSPHORIC ACID AND POT EXPERIMENTS. 
(Contribution from the Texas Agricultural Experiment Station.) 
By G. S. Fraps* 
The problem of establishing a chemical method which shall deter- 
mine what plant food is needed by the soil is an exceedingly impor- 
tant one to the agricultural chemist and to the practical farmer. If 
it should be possible, in the laboratory, to ascertain exactly the 
needs of the soil for plant food, chemical analysis could determine 
the kind of fertilizer which should be added to produce the best 
results, and this would undoubtedly be of vast practical importance. 
EFFECT OF CHEMICAL CONSTITUENTS ON SOIL FERTILITY. 
Before entering upon the solution of this problem, it is well to 
consider whether the chemical constituents of the soil are the only 
factors which control the supply of food to the plant. If chemical 
composition is not the only factor, we must then consider how these 
other factors influence one another, and what information the chem- 
ical analysis can give us. If chemical analysis cannot give us all 
the information we desire, how much information can it give us? 
Obviously, if we know our limitations we shall be less liable to dis- 
appointment in applying our results. 
The conditions of moisture in the soil undoubtedly affect the 
absorption of plant food. A poor soil well supplied with moisture 
may provide more plant food, for a time, at least, than a much bet- 
ter soil under less favorable moisture conditions. Physical condi- 
tions undoubtedly affect the supply of plant food to the roots. 
Particles of plant food enclosed in lumps of soil may be useless for 
the purpose of the plant. Of what avail is a subsoil rich in plant 
food if the roots cannot penetrate into it and secure the food f 
In the case of nitrogen, we know well that the chemical nature 
of the nitrogenous material is only a minor factor in supplying the 
plant with food. The great bulk of the nitrogen is inactive and use- 
less to plants. It must first be converted into ammonia and nitrates 
before it is of service. Bacteria performs this conversion and tem- 
perature, moisture and physical conditions of the soil retard or ac- 
celerate their activity. Nitrates are very soluble and may be washed 
from the soil. Bacteria which transform nitrates and ammonia into 
compounds of little service to the plant are also active in the soil. 
Hence the amount of nitrogen at the disposal of the plant is the 
*State Chemist. 
